The present invention is directed to a process for removing organic foulants from anion exchange resins, such as resin used for polishing condensate water in steam turbine power plant systems.
In many applications, such as for example in steam turbine power plant systems, anion exchange resins and cation exchange resins are used in a polishing system to remove anionic and cationic impurities such as sodium, calcium, magnesium, sulfate and chloride ions from the water. If not removed, these solid forming precursors can produce corrosion within the turbine, boiler and preboiler systems. The exchange resins are used for removing these precursors from both makeup water and condensate water.
The anion exchange resin can be fouled by organic impurities, including organic sulfonates. It is believed that the source of the organic sulfonates is cation exchange resin or organic contaminants left in the cation exchange resin during its manufacture. Organic sulfonate fouling greatly shortens the life of the anion exchange resin.
A brine process has been developed for removing organic foulants from the anion exchange resin used for makeup water. According to this process, as described by Samuel B. Applebaum, Demineralization By Ion Exchange, Academic Press, New York (1968), pages 159-60, the resin is treated with a caustic soda and sodium chloride solution. However, there are difficulties with this brine process. For example, in a typical power plant, there is no convenient source of the sodium chloride solution. Further, this process totally exhausts the resin, which necessitates the expense of having to regenerate the resin with high dosages of chemicals. The resin is exhausted because the cation exchange resin is put in the sodium form and the anion exchange resin is put in the chloride form. Sodium cation resin and chloride form anion resin are difficult to regenerate sufficiently to use for pure water production. Moreover, the organic contamination recently encountered is in the form of organic sulfonates, and it is not known whether the brine process is effective for organic sulfonates. A further problem with the brine process is that it is not useful for removing organic foulants from the anion exchange resin used to polish condensate water because of the cost and inconvenience of the process as well as the cost of adequately regenerating the resin.
Thus, when anion exchange resin used for polishing condensate water becomes fouled with organic foulants, typically the resin is discarded. Fouling of the anion resin can occur in less than six months. Discarding the resin is very expensive since the resin can cost as much or more than $200 per cubic foot. For a typical fossil fuel power generating plant there are two to three anion exchange resin beds, each containing 50 cubic feet ($20,000 worth of resin. For a nuclear power plant, there can be as many as six beds, each containing in excess of 200 cubic feet ($240,000 worth of resin).
Thus, there is a need for an economical process for removing organic foulants from anion exchange resin, and particularly the anion exchange resin used to polish condensate water in a power plant.